Material blenders are known which include a vertically oriented vessel with a centrally mounted lift column for recirculating material within the vessel. Typical examples of such blenders are shown, for example, in U.S. Pat. Nos. 3,276,753; 3,642,178; and 4,194,845.
Gravity type blenders include a vertically oriented vessel with a plurality of downcomers each having inlets at various levels in the vessel. Material in the upper part of the vessel enters the downcomers and flows into a receiving bin or hopper so that material from various levels in the vessel are mixed. In some instances, a material recirculation system is provided. Typical examples of such blenders are shown for example in U.S. Pat. Nos. 3,158,362; 3,216,629; 3,421,739 and 4,068,828.
Apparatus utilizing a bottom fill technique with a central lift column for blending solid particulate material such as plastic pellets are generally shown in U.S. Pat. No. 4,569,596 and U.S. patent application Ser. No. 680,213 filed Dec. 10, 1984, now U.S. Pat. No. 4,573,800, both assigned to the assignee of the present invention. In this type of system, the material to be blended is pneumatically conveyed from a source of material to the bottom of the blender and the energy utilized for conveying the material to the blender is used to lift the material up the central lift column while also entraining material already in the vessel and lifting the same, along with the fresh material, to the top of the vessel and, thereby, blending the material. Top fill techniques are also known in the art.
In order to improve the supply of material from the top of the vessel to the lift column, attempts have been made to utilize recirculation channels or internal downcomers in combination with a central lift or blending column. One such arrangement is shown in U.S. Pat. No. 3,386,707 issued June 4, 1968.
In blenders utilized for blending solid particulate material such as plastic pellets which utilize a gravity type apparatus for recirculating material, it is known that if a vertical recycle channel or downcomer is placed in the blending vessel and that recycle channel includes a plurality of vertically spaced apart openings along its length, material will normally only flow into the channel from the uppermost opening which is buried by the material in the vessel. Thus, despite the several openings in the channel, material only flows into the uppermost opening down through the channel to the outlet of the channel. Once the level of material in the vessel falls below an opening in the recirculating channel, then material will start flowing into the channel in the next lower opening.
It is known from U.S. Pat. Nos. 4,560,285 issued Dec. 24, 1985; 4,068,828 issued Jan. 17, 1978 and 3,216,629 issued Nov. 9, 1965, that, if a baffle is placed in the channel opening, then there will be flow of material into the channel not only from the uppermost channel inlet, but also in all lower channel inlets which include baffles. As used in a gravity type blender, this creates the ability to withdraw material from not only the uppermost point in the vessel, but also from a lower point to thereby improve blending efficiency.
With prior practice, such as illustrated in the above referenced patents, recirculation of the material is typically through an external means whereby material is withdrawn through the channels, supplied to a pneumatic conveying system, and recirculated outside the vessel to the top of the vessel for further blending.
U.S. patent application Ser. No. 848,005, filed Apr. 3, 1986 and assigned to the assignee of the present invention, discloses a vertically oriented vessel with a plurality of recycle channels circumferentially spaced around the inside of the vessel. Each of these channels has a plurality of vertically spaced apart inlet openings each with an adjustable baffle positioned therein. The vessel includes a tubular extension extending downwardly at the bottom of the vessel. A centrally mounted lift or blending column is mounted in the vessel and extends into the tubular extension to define a seal leg. Particulate material to be blended may be supplied either into the top of the vessel or in the preferred form, into the bottom of the vessel for passage directly upwardly through the vertical lift column using the energy used to supply the material to the blender. Material already in the vessel moves by gravity down through the recycle channels to the area of the seal leg for entrainment with incoming material up through the blending column. The outlets of the recycle channels are placed near the top of the seal leg and the inlet for the lift column is placed near the bottom of the seal leg.
The means for controlling the flow of material into the recycle channels includes a moveable flow controlled deflector which may be positioned between extreme positions of extending into the channel or extending out of the channel into the vessel. By the present invention, it has been discovered that if the moveable deflector extends into a channel, material will flow into that channel from both the uppermost opening in the channel and a lower opening. If the moveable deflector extends out of the channel, then material will not flow into that opening unless it is the uppermost opening in the channel. A valve means may be placed in each recycle channel to control flow of material through that channel.
The subject matter of each of the above-noted patents and patent applications is incorporated by reference herein.
In continuous blending systems, it is customary to withdraw blended product from a single location (elevation) within the blender bed. The concentration of ingredients of the effluent then becomes a function of the relative location of the feed and withdrawal points as well as elapsed time. It would, however, be advantageous to withdraw product from a plurality of locations (elevations) within the blender bed.